3(i) Excretion
10 specification points in sub-topic 3(i).
Specification points
3.20: Carbon dioxide and oxygen lost from a leaf
Leaves get rid of oxygen from photosynthesis and carbon dioxide from respiration through stomata.
3.21: Excretory products of the lungs, kidneys and skin
The lungs, kidneys and skin as organs that excrete waste from the human body.
3.22B: Excretion and osmoregulation by the kidney
How the kidneys remove urea and control the water and ion content of the blood.
3.23B: Structure of the urinary system
The urinary system: kidneys, ureters, bladder and urethra and what each does.
3.24B: Structure of a nephron
The parts of a nephron, from the glomerulus and Bowman’s capsule to the collecting duct.
3.25B: Ultrafiltration
Ultrafiltration: how small molecules are forced out of the blood in the glomerulus.
3.26B: Reabsorption of water from the collecting duct
How water is reabsorbed from the collecting duct into the blood by osmosis.
3.27B: Selective reabsorption of glucose
Selective reabsorption: how all filtered glucose returns to the blood.
3.28B: ADH and the water content of the blood
How ADH controls the water content of the blood by negative feedback.
3.29B: Composition of urine
What urine contains, and why its water, urea and salt content changes.